1. Technical Field
Embodiments of the invention relate generally to systems and methods for side-by-side mooring of vessels at an offshore location to minimize relative motions between the vessels and reduce undesirable forces induced by weather conditions.
2. Description of Related Art
Offshore mooring systems have been used to secure two vessels in a side-by-side configuration. In a side-by-side mooring configuration, the vessels respond to changes in environmental conditions as a single vessel. One common problem is the dynamic directional changes in environmental conditions, e.g. wind, wave and/or current, which will increase relative motions between the vessels and mooring forces acting on the fenders and mooring lines between the vessels. In order to minimise relative motions between the vessels and mooring forces acting on the fenders and mooring lines between the vessels, it would be desirable to allow the vessels weather vane such that the heading of the moored configuration is aligned to the prevailing weather condition. This alignment minimises the vessel area exposed to wind, wave and currents which, in turn, minimizes the load on the mooring.
U.S. Patent Application Publication No. US 2007/0289517 A1 (Poldervaart et al.) (hereinafter '517) relates to a mooring system with a first vessel for containing hydrocarbons having at its bow and/or stem a transverse arm and a fluid transfer mechanism of a duct connected to a tank on the first vessel and a coupling end for connecting to a second vessel. The second vessel is moored alongside the first vessel and is attached via at least one cable, extending from its bow in the length direction of the vessel, to a mooring end of the arm. The mooring end of the arm is situated at or near a longitudinal centerline of the second vessel. The arm, during use, is in a fixed position and a pulling force element is attached to the cable for applying a pulling force on the cable upon relative movement of the second vessel with respect to the arm. The force element allows a predetermined maximum displacement of the second vessel.
However, the mooring system of '517 suffers from a number of problems. For example, the mooring system of '517 would not allow complete alignment of the moored configuration to the dominant environmental condition. Further, as the mooring arm of '517 is rigid and is subject to forces induced by vessel motions in six degrees-of-freedom, i.e. surge, sway, pitch, roll, heave and yaw, the mooring arm is prone to damage and breakage.
Accordingly, a mooring system that eliminates the above and other problems of existing mooring systems is highly desired.